Android 应用中的 SharedPreferences 用于记住我按钮

Question

我不确定我做错了什么。在我的应用程序中，我试图让它记住以前在提交时输入文本字段的密码。从使用共享首选项完成的研究中保存变量，即使应用程序重新启动也是如此。我的代码顶部：

public class AK_Voucher_access extends BT_fragment{

View thisScreensView = null;

String errormessage = "";
String errormessageTextColor = "";
String errormessageText = "";
String rememberTextText = "";
String rememberTextTextColor = "";
String voucherTextfieldPlaceholder = "";
String voucherTextfieldSecureTextEntry = "";
boolean voucherTextfieldSecureTextEntryBool = false;
String iphoneImage = "";
String ipadImage = "";
String errormessageInvalid = "";
String errormessageRemember = "";

private TextView errormessageTextView = null;
private EditText voucherTextfieldEditText = null;
private ImageView imageView = null;
private Button submitButton = null;
private Switch rememberSwitch = null;

private Drawable myHeaderImageDrawable = null;
private String alphaImage = "", pass;
private static BT_item screenObjectToLoad = null;
private static final String PASSVALUE = "value";
//private static final String appPassword = "appPassword";
Context context;

设置时检索文本字段：

if (rememberSwitch.isChecked()) {
            BT_debugger.showIt(fragmentName + ":rememberSwitch is ON");

        SharedPreferences settings = context.getSharedPreferences(PASSVALUE, MODE_PRIVATE);

        String rpass= settings.getString("rpassword","");


            if (rpass!=null) {
                    voucherTextfieldEditText.setText(rpass);
            } else {
                voucherTextfieldEditText.setText("nono");
            }

    }
    else {
        BT_debugger.showIt(fragmentName + ":rememberSwitch is OFF");
        // switchStatus.setText("Switch is currently OFF");
    }

然后我的代码在提交时保存字符串：

if (loadScreenNickname.length() > 1 && !loadScreenNickname.equalsIgnoreCase("none")) {

                // before we launch the next screen...
                if (!rememberSwitch.isChecked()) {
                    voucherTextfieldEditText.setText("");
                }

                if (rememberSwitch.isChecked()){
                    //voucherTextfieldEditText.setText("");

                    String pass = voucherTextfieldEditText.getText().toString();
                    BT_debugger.showIt(pass + ":CODE");

                    SharedPreferences settings = context.getSharedPreferences(PASSVALUE, MODE_PRIVATE);
                    settings.edit().putString("rpassword", pass).apply();

                    rememberSwitch.setChecked(true);



                }
                errormessageTextView.setVisibility(View.GONE);
                errormessageTextView.invalidate();

                //loadScreenObject(null, thisScreen);
                try {
                    loadScreenWithNickname(loadScreenNickname);

                    foundIt = 1;

                } catch (Exception ex){
                    Log.e ("eTutorPrism Error", "Caught this exception " + ex);
                    ex.printStackTrace();
                }
                break;
            }
        }

但是超时我运行我的应用程序中的插件我在 logcat 中收到此错误：

E/UncaughtException: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.SharedPreferences android.content.Context.getSharedPreferences(java.lang.String, int)' on a null object reference
                                                               at com.asfapp.ui.bt_plugins.AK_Voucher_access.onCreateView(AK_Voucher_access.java:210)


E/AndroidRuntime: FATAL EXCEPTION: main
                                                        Process: com.asfapp, PID: 24771
                                                        java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.SharedPreferences android.content.Context.getSharedPreferences(java.lang.String, int)' on a null object reference
                                                            at com.asfapp.ui.bt_plugins.AK_Voucher_access.onCreateView(AK_Voucher_access.java:210)

这次不确定代码有什么问题，但任何事情都会有所帮助。

Answer 1

尝试

Context context = getApplicationContext();
SharedPreferences settings = context.getSharedPreferences(PASSVALUE, context.MODE_PRIVATE);

您收到 NullPointerException，因为上下文未定义。在调用 context.getSharedPreference() 之前定义它或使用其他方式，例如 getApplicationContext().getSharedPreference() .

Answer 2

你定义上下文吗？

Context context;

我在这里没有看到上下文的价值。也许这就是它 return NullPointerException 的原因您应该使用 activity 或上下文来定义它。你也可以这样做而不是制作上下文变量： getApplicationContext().getSharedPreferences() 要么 getActivity().getSharedPreferences()

Answer 3

使用此代码在 fragment

中获取 SharedPreference

SharedPreferences preferences = this.getActivity().getSharedPreferences("myPref", Context.MODE_PRIVATE);

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